Adipose tissue cellularity and histochemistry in fetal swine as affected by genetic selection for high or low backfat

Adipose tissue development was studied histochemically and histologically in fetuses from lean and obese sows. At 110 days of gestation, fetuses were removed from Ossabaw (obese-feral) sows and from sows selected for high backfat (obese-domestic) and for low backfat (lean) thickness. Body weights were similar for lean (916 +/- 225 g) and obese (822 +/- 167 g) domestic fetuses, whereas obese feral fetuses were smaller (631 +/- 70 g). Histological and histochemical analysis was conducted on subcutaneous tissue from over the shoulder. Staining for lipid-containing fat cells indicated similar concentrations of fat cells throughout the depth of the subcutaneous tissue from obese (domestic and feral) and lean fetuses. Adipocytes from obese fetuses were slightly larger (domestic 23 +/- 0.22 microns, feral 21.8 +/- 0.26 microns) than cells from lean fetuses (20.7 +/- 0.42 microns). The percentage glycogen positive (PAS) adipocytes was low and similar from all three fetal strains. Less than 10% of adipocytes from lean and obese domestic fetuses were esterase-positive, whereas 42% of adipocytes from obese feral fetuses were esterase-positive. All adipocytes from obese fetuses (domestic and feral) were lipoprotein lipase (LPL)-positive whereas all cells from lean fetuses were negative for LPL activity. Therefore, cellular and metabolic differences exist in adipose tissue of lean and obese pigs during the prenatal period of growth and development.